This application claims priority of European Patent Application No. 99306933.5, which was filed on Aug. 31, 1999.
The present invention relates to cellular radio communication handover systems.
In packet switched cellular radio communication systems, a mobile station sends and receives data to and from a selected cell in discrete packets during a selected time slot of a time division multiplex cycle. Other mobile stations use other slots in the multiplexed cycle. When the mobile station moves to another cell, it effects a handover for transmitting packets of data from the old cell to the new cell.
Using ETSI (European Transmission Standards Institute) standards for General Packet Radio Service (GPRS) or Enhanced General Packet Radio Service (EGPRS) Real Time (RT) service during handover cannot be maintained as EGPRS was primarily designed for Non-Real Time (NRT) data flows. Thus, during the cell handover period, data flow is stopped completely before handover takes place and is only recommenced after handover has been completed. The reliability of Quality of Service (QoS) under these conditions is thus guaranteed over the air (Um) interface using acknowledgements of correct packet transfers with corrupted packets being retransmitted.
The decision to transfer control of data flow from one cell to another in this arrangement is taken by the mobile station rather than the network.
In these circumstances, the packet flow during real time transmissions is interrupted and data is lost because of the long delay over which handover takes place. This will cause some annoyance to the end user of the flow.
Under EGPRS when a mobile station decides that the quality of transmission in a particular cell is becoming poor, it switches to another cell having a better transmission quality. To accomplish this, it puts into effect the following procedures.
1) It aborts any or all xe2x80x9ctemporaryxe2x80x9d block flows (TBF) in progress by immediately ceasing decoding on the downlink (DL) and ceasing to transmit on the uplink (UL).
2) It stops all the mobile timers related to measurement reporting.
3) The mobile station switches to the selected cell obeying all the relevant RLC/RAC (Radio Link Control/Random Access Control) procedures for the new cell; ie it reattaches itself to the new cell by performing a packet channel request on the PACH/PRACH (Packet Access Channel/Packet Random Access Channel) channel.
The net effect of these procedures is that data flow is completely interrupted. Also the mobile station may have to compete for resources in the new cell in order to re-establish data flows thereby increasing the delay still further before data flow can be resumed. It will thus be apparent that the current standards for GPRS and EGPRS do not provide satisfactory QoS for RT transmissions during handover.
According to the present invention there is provided a packet switched cellular radio communication handover system for effecting handover of radio transmissions between a mobile station and one cell of a multicell network to radio transmissions between the said mobile station and other cells of the network, the network having reporting means for causing the mobile station to take and report back measurements on a given list of cells, selection means for selecting a said cell by comparing the measurements with a predetermined criteria, and handover means for forcing the mobile station to handover to the selected cell.
According to the present invention there is further provided a cellular radio communication system for effecting handover of radio transmissions between a mobile station and one cell of a multicell network from said one cell to another cell of the network, the mobile station having a plurality of modes of operation in conjunction with the network including a) mobile station controlled autonomous reselection with no measurements being reported to the network, b) mobile station controlled autonomous cell reselection with a measurement report being transmitted to the network, c) network controlled cell reselection with a measurement report from the mobile station to the network, and d) network controlled real time cell selection with a measurement report from the mobile station to the network.
According to the present invention there is still further provided a cellular communication handover system for effecting handover of radio transmission between a mobile station and one cell of a multicell network to radio transmission between said mobile station and other cells of the network, the network having handover means for forcing the mobile station to handover to a selected cell, the mobile station including mean talk spurt means for establishing the mean talk spurt in the transmissions to and from the mobile station, activity monitoring means for monitoring a predetermined type of activity of the transmitter and receiver of the mobile station, and delay means operable to delay any handover operation while said activity monitoring means senses activity for a period corresponding to the period of the mean talk spurt.